Senior Contract C++ / JavaScript Software Engineer (Browser Engine)

Belgium, Denmark, Finland, France, Netherlands, PolandContract2026-10-27 → 2026-11-10

Core

Improve the health of the Firefox DOM Core Session History area by writing tests, fixing problems, and ensuring Gecko correctness.

Role type

Senior IC browser-engine software engineer (C++/JavaScript)

Builds

Web-Platform tests and Gecko mochitests for the Firefox browser

Domain

Browser engine development (Firefox/Gecko)

Required skills

C++ development, JavaScript (for automated testing), debugging in large codebases, code review, Web-Platform test writing

Preferred skills

Prior contributions to Gecko or major browser engines, familiarity with web standards and Web Platform Tests

Technologies

C++, JavaScript, Gecko, Web-Platform Tests, mochitests

Responsibilities

Write Web-Platform tests to improve coverage, fix problems to improve Gecko correctness, work through code review with module owners

Seniority

Senior, hands-on IC

About Mozilla

Mozilla exists to build the Internet as a public resource accessible to all because we believe that open and free is better than closed and controlled. When you work at Mozilla, you give yourself a chance to make a difference in the lives of Web users everywhere. And you give us a chance to make a difference in your life every single day. Join us to work on the Web as the platform and help create more opportunity and innovation for everyone online.